The present invention relates to improved three-dimensional battery electrode substrate materials and, more specifically, to a nickel electrode substrate which provides enhanced active substrate filling and retention within the electrode matrix and which permits enhanced mechanical strength and integrity during cell construction and reduced shorting between electrode layers in the cell after fabrication, thus enhancing cell manufacturing yield.
At present, rechargeable battery electrode substrates are manufactured from a wide variety of reticulated metal foams or sponge-type metal materials, metal fibers and metal powder compacts. Specifically, nickel three-dimensional battery electrodes (metal fibers) are made primarily through a sintering process utilizing a felt-type conductive porous material composed of nickel fibers and nickel powder, such, as carbonyl nickel powder. The resultant nickel battery electrodes generally contain between 75-90 weight percent nickel fiber and 10-25 weight percent nickel powder. An example of such a battery electrode is described in Japanese Patent Publication 63-12473. This publication discloses a felt-type nickel battery electrode containing long nickel fibers and nickel powder. In such an electrode, the fiber and powder provide a porous material having cavities or voids therein which on average are approximately 60 microns in diameter. After sintering of the fiber and powder porous material, the active chemicals such as, nickel and cadmium hydroxides are added or loaded into the porous material to generate the electrical energy of the battery electrode by chemical reaction. The active chemicals are loaded or added to the fiber substrate or matrix by a number of techniques, including chemical or electrochemical conversion and mechanical injection of high viscosity aqueous pastes of the active materials or chemicals.
As the demand for higher capacity electrodes has increased, the prior art three-dimensional battery materials or substrates and, in particular, the prior art porous matrices or structures comprising sintered long nickel fibers and nickel powders have been found to be only partially effective in that the nickel powder contained within the fibrous substrate tends to block the entry of active chemicals into the possible loading areas within the fiber matrix. Accordingly, the reticulated metal foams, metal fiber and powder compacts, in accordance with the prior art, appear to exhibit a porosity of a level which restricts the penetration of the active chemical or chemicals to the center of the matrix, and which limits the amount of active chemicals that may be loaded into the matrix, thus resulting in reduced electrode efficiency.
A further disadvantage of such prior art three-dimensional electrode substrate structures is that the metal fiber matrix is composed of fiber lengths exceeding about a quarter and a half inch in length. It is believed that this length of long fiber was desirable to facilitate distribution of the active chemical space throughout the fiber matrix to provide an overall fiber matrix containing a predetermined weight of fiber material. Also, it has been found that the subsequent processing of such metal fiber matrices, metal foams and metal powdered compacts and layering of the electrode material results in an electrode material which possesses inadequate tensile strength and ductility, which substantially reduces the production yield of material which may be spiral-wound into cells for insertion into the completed electrode assembly.
Additionally, such prior art three-dimensional spiral-wound electrode materials possess substantial fiber ends rising from the spiral-wound surface or surfaces of the completed electrode assembly, a problem which results in a brittleness in bending which substantially increases the amount of breaking during processing of the electrode. Furthermore, the loose fiber ends and broken fibers extending from the surface of the spiral-wound electrode, which ends often times penetrate the separator material thereby resulting in a shorting out between electrodes of the finished battery assembly.